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Plants on the move

FOR the past two million years or so, what’s called the Quaternary period,
the Earth’s climate has blown both hot and cold. So far, it has fluctuated from
cold ice age or glacial period to warm interglacial period some 50 times during
the Quaternary, with the last ice age ending 10 000 years ago.

Vast ice sheets formed over huge areas of Northern Europe and North America
during the cold phases. These left many telltale marks, typically deep U-shaped
valleys with scarified rock surfaces and basins filled with water, forming deep
lakes. Much of the land that was once blanketed …